1. Field of the Invention
This invention relates in general to wireless communications systems, and more specifically, to a dispatch service providing “push-to-talk” service in a cellular telephone system.
2. Description of Related Art
Group-based dispatch services (two-way half-duplex voice calls within a group also known as “Push-to-Talk” or PTT) have enormous revenue earnings potential for wireless networks, such as cellular networks and personal communications systems (PCS) networks. Corporate subscribers primarily use such services for coordinating field people or fleet users from a central location.
Currently, there are two major approaches employed in providing dispatch services such as PTT in wireless networks. One approach requires the installation of a dedicated private network, parallel to the wireless network, to support dispatch services. Nextel™ uses such a system, based on a solution developed by Motorola™ known as iDEN™. However, a dedicated private network is costly to install and maintain employed by a few public wireless carriers,
Another approach is based on Voice over IP (VoIP) technologies. While this approach promises compliance with newer and emerging standards, such as GPRS (General Packet Radio Service), UMTS (Universal Mobile Telecommunications System), etc., it does not provide a solution for carriers employing wireless networks based on existing standards, such as GSM (Global System for Mobile Communications), CDMA (Code Division Multiple Access), etc. Even for the newer standards, solutions based on VoIP have serious drawbacks as explained below.
1. Call Setup: VoIP based solutions suffer from slower call setup, since this is a serial process. For example, for a CDMA PTT solution, call setup involves a CDMA data channel setup, followed by a PTT setup with SIP (Session Initiation Protocol) signaling. There is a need, instead, for parallel call setup exploiting existing cellular solutions.
2. Maximum Information Throughput Rate: VoIP solutions result in significant overhead to carry voice over data channels resulting in significantly reduced net information throughput rate.
3. Impact of Packet Loss: VoIP solutions employ voice packet aggregation that results in increased susceptibility to packet losses.
4. Voice Quality: VoIP solutions employ low bit rate voice coders (4 kbps). There is a need, instead, for an approach that complies with higher rate voice coders, such as EVRC (Enhanced Variable Rate Codec), resulting in better voice quality.
5. Impact to Mobile Handsets: VoIP solutions require significant modifications to the mobile handset. There is a need, instead, for solutions that require only minimal upgrades to the handset.
In summary, there is a need in the art for dispatch services solutions that comply with existing and emerging wireless standards and provides superior user experience with faster call setup, better voice quality, and improved information rate compared to other competing solution.
The present invention aims to satisfy these needs by providing group-based dispatch services that use existing networks with minimal changes. The dispatch service architecture framework of the present invention allows the wireless network to provide an instantaneous voice messaging service wherein a group of users can exchange voice messages at any time from anywhere within the network. This powerful, innovative and cost-effective dispatch service architecture framework will differentiate the service offerings by present wireless networks and provide them edge over their competitors.